I have edit some of the part, I checked the track offset about 4-9m this is accepetable range.

Sometime due receive signal of the device are not so accurate, is hard to say which one is best accuracy when tracked road offset 1-10m. Different devices have different accuracy, I tested oregon, nuvi 760 and nuvi 255w, all track in same time but have different offset.

The best way to check offset are, track near by places have crossing north to south and east to west, need to 2 track like this to check the offset, if not there difficult to check.